Plan B Pill - What Is It & How Does it Work

Morning After Pill (Plan B) – All Your Questions Answered

Medically Reviewed By
Dr. Sanjana Sainani (Gynecologist/Obstetrician)
View more Gynecologist/Obstetrician Our Panel of Experts

The Plan B pill also called the morning-after pill, is usually the first thing women turn to after unprotected sex. When taken right, within a stipulated period of time, the pill can prevent any unwanted pregnancy. Many women have a lot of questions when it comes to the pill, regarding its safety, effectiveness and more. Here is a complete set of information about the Plan B pill, how it works, its success rate and everything in between.

What is the Plan B/ One-Step/ Morning After Pill?

Plan B one-step pill is an emergency contraception pill that can be used after having unprotected sex. It is also called the morning-after pill. However, it is best to take the pill immediately after you engage in unprotected sex to increase its effectiveness.

How Effective is the Plan B Pill?

The Plan B pill, when taken within the duration of 72 hours after engaging in unprotected sex, is about 89% effective. When taken within 12 hours after sex, it can lower the chance of pregnancy by about 95%.

How Does the Plan B Pill Work?

Plan B one step is a single tablet emergency contraception that has levonorgestrel, which is a female hormone responsible for prevention ovulation. This hormone can prevent the ovary from release an egg or make it harder for the sperm or the fertilized egg to get to the uterus by causing changes in the lining of the uterus and the cervical mucus.

Levonorgestrel is the same hormone used in birth control pills, but Plan B has a higher dose of it, about 1.5 milligrams.

Taking the Morning-After Pill

The important thing to remember about the Plan B pill is, the sooner the better. Here is more information about when and how you should take the pill.

Who Should Take the Morning-After Pill

The morning after pill is ideal for women who have missed their birth control pills or faced a failure using birth control methods, like tearing of the condom or if you haven’t used birth control.

When to Take the Morning-After Pill

The Plan B pill should be taken within 72 hours of unprotected sex. The sooner you take it the better is its effectiveness in preventing pregnancy.

How to Take the Plan B Pill

Plan B is a single-dose oral pill that needs to be consumed within 3 days (72 hours) after having unprotected sex. Hence, it is best to have it ready to prevent any delay.

When to Avoid Taking the Plan B Pill

It is best to avoid Plan B when you are pregnant, as it will not be effective. Also, do not use the pill if you are allergic to levonorgestrel or other components in the pill. Women who weight over 75 kg or 165 lb may find that Plan B isn’t very effective. This is because women who are overweight produce more drug metabolising enzymes through the liver reducing the effectiveness of the pill.

How Often Can You Take Plan B?

Plan B should only be taken when your regular birth control pills and methods fail. It is an emergency pill and is effective only when taken immediately after unprotected sex or in the event that birth control methods have failed. It does not offer any protection as a long-term contraceptive.

Is it Safe to Take Plan B With Your Regular Birth Control Method?

Plan B only works if taken after unprotected sex and is not effective if taken before engaging in unprotected sex.

It is safe to take Plan B even if you are using regular birth control pills, in the event that you’ve missed a few doses. However, it should never be used in place of regular birth control pills.

Plan B Side Effects

Plan B is generally safe when taken as per the directions. Some of the possible side effects include:

  • Nausea
  • Unusual flow, heavier or lighter than normal
  • Irregular periods, earlier or later than normal
  • Lower abdominal cramps
  • Headache
  • Dizziness
  • Tenderness in the breast
  • Vomiting
  • Fatigue

Side effects: Vomiting

The pill may cause some unexpected bleeding or spotting in some women during the interval before their next period. If you find that your period is delayed by over a week, then you will need to check with a doctor and get a pregnancy test.

Also, in case you vomit within two hours of taking the pill, you should consult your doctor and ask if another pill needs to be taken.


While the pill is largely safe for most women, you may need to keep in mind a few things to prevent any potential complications.

Drugs that Affect the Morning-After Pill

It is always recommended that you keep your doctor informed about all the drugs that you are using. Do not use an over-the-counter drug if you are already under medications.

Some of the drugs or herbal products that may interfere with the effectiveness of the Plan B pill are:

  • Rifampin like Rifadin, Rifamate, Rifater, Rimactane
  • barbiturates such as amobarbital (Amytal), mephobarbital (Mebaral), phenobarbital (Luminal, Solfoton), butabarbital (Butisol), or secobarbital (Seconal).
  • medications prescribed for seizures like phenytoin, or carbamazepine
  • bosentan
  • griseofulvin
  • oxcarbazepine
  • felbamate
  • St John’s wort
  • Topiramate
  • Certain HIV/AIDS medications

What if You are Already Pregnant and Take the Morning After Pill

Taking the morning-after pill when you are already pregnant will not have any effect at all. Pregnant women who take the pill will find that the treatment is ineffective and it does not cause harm to the development of the baby.

How Soon Will You Gain Your Fertility After Taking Plan B?

Plan B prevents ovulation for the cycle that you take the pill for and your fertility will return to normal within the next cycle. Hence, it is best if you start using regular birth control pills as soon as possible, as the pill you took won’t be able to protect you from unprotected sex during that cycle.

Other Important Information:

Here is some more information about the Plan B pill that may be helpful.

How to Know if the Morning-After Pill Worked

You will know that the pill has worked when you get your next period at the regular time. In case your period is delayed by a week or more, it is recommended that you take a pregnancy test or consult a doctor as there are chances that you may be pregnant.

Plan B will is likely to not work if you have had unprotected sex earlier in the cycle. The pill also doesn’t protect you from unprotected sex again in the same cycle, as one pill protects against one instance of unprotected sex. It may also not work if you vomit within two hours or taking the pill. In this case, you may talk to your doctor about taking another pill.

How Long After Taking Plan B One-Step Can You Resume Your Regular Contraceptive?

You can take your birth control pills on the same day that you’ve taken the Plan B. It is important to take get back to your regular contraceptive pills to avoid getting pregnant in case you have unprotected sex within the same cycle.

What if You Miss the Dose

If you miss the dose and are not able to get your hands on a Plan B within 72 hours after having unprotected sex, your risk of getting pregnant will increase considerably.

A woman consulting doctor a missing dose

During this event, it is advised to consult a doctor immediately to discuss any other options.

Does Plan-B Protect Against Sexually Transmitted Infections (STI’s)?

No. Plan B does not prevent you against any STIs or HIV/AIDS. It is always safe to use a condom during sex to prevent contracting STIs. It may also be beneficial if you and your partner have an open conversation about STIs and get tested and treated.

When is the Morning After Pill Less Likely to Work?

Plan B is less likely to work if you take it later than 72 hours after pregnancy. The pill is also not effective if you are already pregnant. It is also not likely to work in women who are overweight and weigh over 165lb or 75 kg. It is absolutely not effective in women who weigh more than 175 lb or over 80kg.

Where Can You Buy Plan B and How Much Does it Cost?

Plan B can be bought over-the-counter at drugstores. It does not require any prescription and has no age limit. It costs about Rs. 75 at the drugstore.

Emergency contraception options like the Plan B pill are a boon to many women who want to prevent unwanted pregnancy that may stem out of unprotected sex. When taken the right way, within the right duration, it can be quite effective for many women. However, it is important to understand that it only offers protection for a specific time period and cannot be used as a regular method of contraception. Also, it is always best to ensure proper protection and safety during sex to avoid instances of unprotected sex and pregnancy scares.

Also ReadUnderstanding & Using a Birth Control Patch

Previous article «
Next article »